The present invention relates generally to induction heating cooking apparatus, and in particular to a multiple-load induction heating cooking apparatus.
Attempts have been made to provide multiple-load induction heating using a single high frequency source. U.S. Pat. No. 3,925,633 discloses such induction heating apparatus in which two or more commutation circuits each including an induction work coil and a capacitor are connected in parallel to a high frequency energy source. A gate-controlled interconnecting device is provided between each commutation circuit and the high frequency energy source to control the energization period of the work coil. The high frequency source, which is usually comprised of at least a gate-controlled switching device or power-rated thyristor, is interrupted at a low frequency rate to permit the gate-controlled interconnecting device to automatically turn off to regulate the power transferred to the load. However, undesirable consequences such as interference between two or more commutation circuits is likely to result from the fact that the commutation circuits are connected in parallel to the high frequency source. The problem of such interference becomes particularly severe when the magnitude of a load inductively coupled to one of the work coils is much greater than the load associated with the other work coil, particularly when one of the coils is inductively coupled to a substantial load while no load is placed over the other energized work coil. Such interference draws a large current from the power rated thyristor of the high frequency source and results in instability of the frequency and waveform of the energization current oscillated through the commutation circuits.